In an automobile there are numerous actuators such as motors, pumps and fans. Due to increased environmental concerns and emission regulations, there are efforts underway to convert the fixed speed, on/off controlled drives and hydraulic systems for such actuators to more efficient adjustable speed electric drives. This would help improve fuel economy and, therefore, reduce undesirable emissions.
These drives are useful in high performance applications, such as electric active suspension, to meet customer demands. Adjustable speed A.C. motor drives consist of DC/AC inverters, and switching power supplies and controlled rectifiers employ DC/DC converters. All these power electronic circuits consist of power devices arranged in certain circuit configurations. An effort to add the power devices, gate drivers and protection circuits would substantially increase the complexity, cost and packaging disadvantages that offset convenient implementation of such features.
In motor vehicles, these modules have to operate in harsh environments. External causes of stress, such as, temperature, humidity, salt spray, etc. can accelerate the various internal failure modes such as power device failure, transistor stack failure, gate drive failure, power failure and erroneous input commands, in addition to the internal factors of the module. While previously known detectors may warn of current conditions, the condition of the power module has not been reported to the controller periodically in a manner that would allow the controller to anticipate problems, make intelligent decisions and inform the driver of any problems or servicing requirements that a diagnosis may suggest.
The types of failures can be classified as open circuits, short circuits and slow deterioration. Open circuit faults are caused by broken wirebonds, loose terminals or physical degradation. Short circuit faults result from failed devices, thermal melt down or edge termination failures. Slow deterioration of the module could result from the influence of the external ambient factors. In any event, it is difficult to track many failure mechanisms, particularly the numbers of or degrees of failure in the system over its lifetime, although certain electrical parameters and temperature can be monitored by previously known devices.